Supercritical carbon dioxide extraction (SCDE) technique was used to extract essential oils of Origanum vulgare L and Forsythia suspensa. The minimum inhibitory concentrations (MIC) of Origanum vulgare L essential oil and Forsythia suspensa essential oil used alone and in combination were determined by the same geometric dilution method, respectively. Then the synergistic antimicrobial effect of two essential oils was evaluated according to the calculated FIC values. The results showed that in light of the criteria of fractional inhibitory concentration (FIC), the combined use of Origanum vulgare L and Forsythia suspensa essential oils had synergistic effect on three bacteria (FIC=0.2-0.4) and on two mildews (FIC=0.1), and additive effect on two yeasts (FIC=0.8).